Magnesium ethoxide having a high coarse particle content, process for its preparation and its use

ABSTRACT

Particulate magnesium ethoxide having a high coarse particle content can be obtained in a simple and economical manner by the present invention, which provides a process for preparing particulate magnesium ethoxide having a coarse grain content, and includes reacting metallic, optionally activated, magnesium with liquid ethanol under pressure at a temperature above 78° C. The present invention also relates to particulate magnesium ethoxide having a coarse grain content, which contains:  
     &lt;40% by weight of a screening fraction ≦500 μm and  
     ≧60% by weight of a screening fraction &gt;500 μm.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a particulate magnesium ethoxidehaving a coarse particle content, to a process for its preparation andto its use.

[0003] 2. Discussion of the Background

[0004] Processes for preparing magnesium ethoxide have been known for aconsiderable time. One industrial preparation route is the directsynthesis from metallic magnesium and ethanol. This is described, forexample, by H. D. Lutz in Zeitschrift for anorganische und allgemeineChemie, Volume 356, 1968, pages 132 ff. A catalyst is typically requiredto start the reaction and, generally, iodine is used as the catalyst.Magnesium ethoxide prepared in this manner disadvantageously includestraces of the starter catalyst, which can have adverse consequences, forexample, when the resultant magnesium ethoxide is used as a catalystprecursor for Ziegler catalysts or for book preservation. If catalystsare not used, however, the reaction between ethanol and magnesium is notreliably initiated; and uncontrollable initiation behavior inheres greatrisk in industrial processes.

[0005] In the known processes for preparing magnesium ethoxide, longreaction times are also economically prohibitive. For example, for thecomplete reaction of ethanol magnesium to occur, reaction times of morethan 24 hours are required. If the reaction is terminated prematurely,incompletely reacted metallic magnesium remains in the mixture togetherwith magnesium ethoxide; and separation cannot be reasonably carried outwith standard equipment. In addition, the metallic magnesium impairs theproperties of magnesium ethoxide.

[0006] Finally, the synthesis of magnesium ethoxide by known processesalways produces magnesium ethoxide having considerable amounts ofundesirable, undersized grains. This fine grain or dust content likewiseimpairs the properties of the product. This product content can beremoved only with a great deal of expense during the preparation ofmagnesium ethoxide, for example by sieving or classifying, anddiscarding. It is desirable, therefore, to provide a process whichenables the production of magnesium ethoxide in a particularlyeconomical manner.

SUMMARY OF THE INVENTION

[0007] Accordingly, one object of the present invention is to provide amagnesium ethoxide having a high coarse particle content in a simple andeconomic manner.

[0008] Another object of the present invention is to provide a processfor making a magnesium ethoxide having a high coarse particle contentthat is simple and economically feasible.

[0009] Surprisingly, it has now been found that particulate magnesiumethoxide having a high coarse particle content can be obtained in asimple and economical manner by the present invention, the firstembodiment of which relates to a process for preparing particulatemagnesium ethoxide having a coarse grain content, including reactingmetallic, optionally activated, magnesium with liquid ethanol underpressure at a temperature above 78° C.

[0010] Another embodiment of the present invention relates to aparticulate magnesium ethoxide having a coarse grain content, whichcontains:

[0011] <40% by weight of a screening fraction ≦500 μm and

[0012] ≧60% by weight of a screening fraction >500 μm.

[0013] The process according to the present invention can be reliablystarted in a simple and economical manner and without a catalystcontaminating the product. In addition, the present process cancompletely avoid the unwanted residue of incompletely reacted metallicmagnesium. The reaction times of the present process are generallymarkedly less than 24 hours, which inheres a particularly economicalmode of operation. Furthermore, a product having a comparatively lowcontent of unwanted undersize grain or dust content is obtained.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription of the preferred embodiments.

[0015] Preferably, in the process according to the present invention,metallic, optionally activated, magnesium is brought into contact withanhydrous ethanol in the liquid phase under pressure at a temperatureabove the boiling temperature of ethanol at atmospheric pressure (78°C.), the mixture is reacted to completion and the product is isolated.

[0016] Preferably, in the reaction according to the invention, liquidethanol and solid metallic magnesium are brought into contact and heatedunder pressure to a temperature above 78° C. in such a manner thatliquid ethanol is available as a reaction partner, and the hydrogen thatis formed is ejected from the reaction space.

[0017] Preferably, to carry out the reaction according to the invention,dried ethanol is used in excess, so that ethanol can simultaneouslyserve as solvent. The magnesium ethoxide arising in the reactionaccording to the invention is then preferably isolated by filtration orby concentrating the product mixture at a temperature in the range from0° to 180° C. under reduced pressure. More preferably, the isolationtemperature ranges from 5 ° to 150° C., even more particularlypreferably 10° to 125° C., and most preferably 15° to 100° C. Prior toproduct isolation, the resulting product mixture can be preferablycooled to a temperature of 20° to 78° C. More preferably, the coolingtemperature ranges from 25° to 75° C., even more particularly preferably30° to 70° C., and most preferably 35° to 65° C.

[0018] Preferably, both the reaction according to the invention and theisolation of the magnesium ethoxide according to the invention arecarried out under a protective gas. A CO₂-free protective gas which hasbeen dried in a manner known per se is preferably used, for examplenitrogen or argon. Nitrogen, dried and CO₂-free, is most preferred.

[0019] Most preferably, the present invention relates to a process forpreparing particulate magnesium ethoxide having a coarse grain content,wherein metallic, optionally activated magnesium is reacted with ethanolin the liquid phase and subsequently the magnesium ethoxide is isolated,which includes carrying out the reaction under pressure at a temperatureabove 78° C.

[0020] Preferably, in the process according to the invention, thereaction temperature is set to a value of from >78 to 200° C.,particularly preferably from 80 to 130° C., very particularly preferablyfrom 100 to 130° C., and the pressure in the reaction space is set to avalue above 1 bar absolute, particularly preferably to a value of from 2to 6 bar absolute.

[0021] The metallic magnesium used in the process according to theinvention preferably has a particle size of from 20 to 5000 μm.Preferably, it is used as pure magnesium metal. However, before thereaction, it can also be activated, for example by etching.

[0022] To start the reaction, a catalyst may be preferably added to thereaction mixture. The catalyst is preferably made of an inorganic ororganic halogen compound, preferably a mercury halide, an inorganic ororganic acid, such as HCl or acetic acid, or an alkyl orthoformate, suchas tetraethyl orthoformate (TEOF).

[0023] Preferably, in the process according to the invention, thereaction is started by raising the temperature briefly to above 78° C.,and more preferably >90° C. Preferably, in the further course of thereaction, the peak of hydrogen development proceeds at a temperaturebelow 90° C.; the resulting hydrogen is conducted away from the reactionspace; and the remaining reaction proceeds at a temperature above 90°C., likewise with ejection of the hydrogen formed. Preferably, thereaction has generally proceeded quantitatively after 16 hours, so thatin an advantageous manner, virtually no magnesium metal residues remainin the product mixture. The product is generally isolated from theproduct mixture in the manner described above.

[0024] Particulate magnesium ethoxide prepared according to theinvention advantageously has a high content of coarse grains. The graincontent is generally determined under dry protective gas by screeninganalysis according to the usual methods.

[0025] The present invention therefore also relates to a particulatemagnesium ethoxide having a coarse grain content by weight, containing<40% of a screening fraction ≦500 μm (mesh width) and ≧60% by weight ofa screening fraction >500 μm.

[0026] Preferably, magnesium ethoxide according to the inventioncontains ≧80% by weight of a screening fraction >500 μm (mesh width).

[0027] Most preferably in the magnesium ethoxide according to theinvention, the content of a screening fraction >800 μm (mesh width) ismore than 40% by weight, based on the total amount.

[0028] In addition, magnesium ethoxide according to the inventionpreferably contains less than 10% by weight, particularly preferablyfrom 0.01 to 5% by weight, of a screening fraction <315 μm (mesh width).That is to say that particulate magnesium ethoxide according to theinvention has a high content of coarse grain, which is very desirableand particularly economical; and, in a particularly surprising andadvantageous manner, only a comparatively low content of undersizegrain, and the content of fine dust virtually (and desirably)approaching zero.

[0029] Preferably, the process according to the invention is carried outas follows: nitrogen, anhydrous ethanol and particulate metallicmagnesium are introduced under a dry protective gas atmosphere into aheatable stainless steel pressure reactor equipped with an adjustableoverpressure valve, and the mixture is heated to a temperature above 78°C. A pressure above ambient pressure can develop in the sealed reactorowing to the vapor pressure of the ethanol used and the development ofhydrogen according to reaction 1.

Reaction 1

Mg+2C₂H₅OH→Mg(OC₂H₅)₂+H₂

[0030] If this exceeds the limit set at the overpressure valve, thevalve can open and hydrogen and ethanol vapor may escape. The expandedgas mixture is generally passed through a cooler, with ethanolcondensing, while hydrogen is conducted away in a gaseous state. Thecondensed ethanol can be recirculated to the reactor via a metering pumpwhich can overcome the overpressure prevailing in the reactor. Thisreaction procedure has the particular advantage that it is not necessaryto use a condensation system suitable for overpressure. If anoverpressure safe condensation system is available, the overpressurecontrol valve can likewise be mounted at the top of the condensationsystem in such a manner that the expanded gas downstream of the pressurecontrol valve principally contains hydrogen. The condensation systemreflux, ethanol, is generally recirculated to the reactor, so thatrecycling of ethanol with overcoming of pressure can be avoided.

[0031] Preferably, the reaction can also be started at atmosphericpressure, e.g. with the use of catalysts known from the literature, suchas halogens, halogen compounds, acids, mercury compounds or alkylorthoformates, and can then be continued with an increase in pressure.This generally has the advantage that pressure peaks caused by theinitially very vigorous reaction at elevated temperature (>78° C.) canbe made less extreme. An unmanageable pressure increase in the reactorrepresents a considerable hazard potential.

[0032] A further preferred method for the reaction procedure includesbeginning the reaction in the absence of catalyst at atmosphericpressure and the boiling temperature of ethanol (78 ° C.) and increasingthe pressure and temperature in the plant as the reaction progresses.Pressure peaks can likewise be avoided in this manner. If problems withrespect to initiating the reaction should exist, the reaction can bestarted by a brief increase in the temperature and pressure. Immediatelyafter the start of the reaction, uncontrolled hydrogen development canbe checked by decreasing the pressure and temperature in the reactor byexpansion via the pressure control valve.

[0033] The product is preferably isolated in the process according tothe invention in the above-mentioned manner.

[0034] In addition, the process according to the invention has theadvantage that when particulate magnesium having a mean particlesize >200 μm, preferably ≧800 μm, is used, the reaction time is lessthan 24 hours, no metallic magnesium remains in the product andsignificantly fewer undersize grain are produced than when the productis prepared at atmospheric pressure by conventional processes.

[0035] Preferably, the particulate magnesium ethoxide according to theinvention having a coarse grain content, on account of its advantageousproperties, is particularly suitable as a precursor for Ziegler-Nattacatalysts, as a precursor for ceramics and a precursor for bookpreservation media.

EXAMPLES

[0036] Having generally described this invention, a furtherunderstanding can be obtained by reference to certain specific examples,which are provided herein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

Reaction Apparatus

[0037]1-1 stainless-steel autoclave with close-clearance agitator,pressure measuring device (aneroid manometer), temperature measuringdevice (Pt 100 sensor, temperature control via thermostat, liquidmetering pump (diaphragm pump Prominent Gamma/4-/, adjustableoverpressure valve, condensation system (intensive glass cooler), gasmeter (drum gas meter TG3, Ritter) and protective gas blanketing(nitrogen).

Drying Apparatus

[0038] Protective gas (nitrogen)blanketed laboratory rotary evaporator(2-1 glass evaporator flask) with vacuum facility.

Reaction Procedure

[0039] 24.3 g of particulate metallic magnesium (d50 >800 μm,purity: >99%) are introduced together with 356 g of ethanol under aprotective gas curtain into a stainless-steel autoclave. After sealingthe apparatus, the overpressure valve is set to the desired internalreactor pressure and the mixture is brought to reaction temperature. Onreaching the preset temperature and the preset pressure, hydrogen andethanol vapor escape via the pressure control valve into thecondensation system. Ethanol condensed out is pumped back into thereactor via the diaphragm metering pump at the rate at which condensateis formed in the cooler. The resulting hydrogen is removed from thereaction apparatus via the drum gas meter. The volumetric flow rate ofhydrogen is measured. If hydrogen development can no longer be observed,the reaction is terminated by depressurizing and cooling the reactor.The suspension (magnesium ethoxide in ethanol) is transferred to the 2-1flask of the rotary evaporator and dried there in the course of 2.5hours at 100° C. and under reduced pressure (to 1 mbar). The product isthen subjected to a particle size analysis (screening analysis). Inaddition, the content of incompletely reacted metallic magnesium isdetermined indirectly from the amount of hydrogen formed on addingaqueous hydrochloric acid to the product.

[0040] 1. (NP6994) Preparation of magnesium ethoxide from ethanol andmagnesium at 110° C. and a pressure of 3 bar

[0041] The procedure as described under “reaction procedure” isfollowed. The temperature of the heating medium (silicone oil) of thethermostat is 170° C. At a pressure of 3 bar in the reactor, thetemperature in the reactor is 110° C. Approximately 5 minutes afterreaching the reaction temperature, the maximum hydrogen development ofapproximately 30 1/h is measured. The reaction is complete afterapproximately 6 hours; no more hydrogen development occurs. The productis dried and analyzed as described above. Screening Analysis >800 μm55.7% by weight 500-800 μm 36.4% by weight 315-500 μm 7.1% by weight200-315 μm 0.6% by weight 100-200 μm 0% by weight <100 μm 0.1% by weightMetallic Magnesium <0.02% by weight

[0042] 2. (NP6694) Preparation of magnesium ethoxide from ethanol andmagnesium at 120° C. and a pressure of 4 bar

[0043] The procedure as described under “reaction procedure” isfollowed. The temperature of the heating medium (silicone oil) of thethermostat is 170° C. At a pressure of 4 bar in the reactor, thetemperature in the reactor is 120° C. Approximately 5 minutes afterreaching the reaction temperature, the maximum hydrogen development ofapproximately 35 1/h is measured. The reaction is complete afterapproximately 3.5 hours; no more hydrogen development occurs. Theproduct is dried and analyzed as described above. ScreeningAnalysis >800 μm 46.2% by weight 500-800 μm 36.4% by weight 315-500 μm13.1% by weight 200-315 μm 3.3% by weight 100-200 μm 0.8% by weight <100μm 0.1% by weight Metallic Magnesium <0.02% by weight

[0044] 3. Preparation of magnesium ethoxide from ethanol and magnesiumat 78 ° C. and atmospheric pressure (1 bar, comparative example, NP6894)

[0045] The procedure as described under “reaction procedure” isfollowed, but with the difference that the magnesium turnings used arewashed with 0.1 N aqueous HCl to remove the oxide layer and dried underprotective gas at 100° C. to increase the reactivity; the reaction isnot reliably initiated without this step. The temperature of the heatingmedium (silicone oil) of the thermostat is 120° C. At a pressure of 1bar in the reactor (atmospheric pressure), the temperature in thereactor is 78° C. Approximately 5 minutes after reaching the reactiontemperature, the maximum hydrogen development of approximately 6 1/h ismeasured. After approximately 7 hours, a sample is taken from thereactor. The reaction product still contains considerable amounts ofincompletely reacted magnesium which is visible to the eye. Hydrogendevelopment is not complete until after a reaction time of more than 24hours, and the reactor is cooled. The product is dried and analyzed asdescribed above. Screening Analysis >800 μm 5.9% by weight 500-800 μm39.5% by weight 315-500 μm 42.9% by weight 200-315 μm 8.6% by weight100-200 μm 2.6% by weight <100 μm 0.5% by weight Metallic Magnesium<0.02% by weight

[0046] The particle size distribution shows a marked increase ofunwanted undersized grain (content of particles <315 μm is >11%).

[0047] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

[0048] This application is based on German patent application DE19849353.3, filed Oct. 27, 1998, the entire contents of which are herebyincorporated by reference.

1. A particulate magnesium ethoxide having a coarse grain contentcomprising: <40% by weight of a screening fraction ≦500 μm and ≧60% byweight of a screening fraction >500 μm.
 2. The particulate magnesiumethoxide as claimed in claim 1 , comprising <10% by weight of ascreening fraction <315 μm.
 3. The particulate magnesium ethoxide asclaimed in claim 1 , comprising from 0.01 to 5% by weight of a screeningfraction <315 μm.
 4. The particulate magnesium ethoxide as claimed inclaim 1 , comprising ≧80% by weight of a screening fraction <500 μm. 5.The particulate magnesium ethoxide as claimed in claim 1 ,comprising >40% by weight of a screening fraction >800 μm.
 6. Theparticulate magnesium ethoxide as claimed in claim 1 , which is producedby a process comprising reacting metallic, optionally activated,magnesium with liquid ethanol under pressure at a temperature above 78°C.
 7. A process for preparing particulate magnesium ethoxide having acoarse grain content, comprising: reacting metallic, optionallyactivated, magnesium with liquid ethanol under pressure at a temperatureabove 78° C.
 8. The process as claimed in claim 7 , wherein the liquidethanol and metallic magnesium are contacted with one another in areaction space, heated under pressure to a temperature above 78° C.,wherein the liquid ethanol is available as a reaction partner, andwherein hydrogen is formed and ejected from the reaction space.
 9. Theprocess as claimed in claim 7 , wherein the reaction temperature isfrom >78 to 200° C. and the pressure in the reaction space is above 1bar absolute.
 10. The process as claimed in claim 7 , wherein thereaction pressure is above 1 bar absolute.
 11. The process as claimed inclaim 7 , wherein the metallic magnesium has a particle size of 20 to5000 μm.
 12. The process as claimed in claim 7 , further comprisingraising the temperature to above 90° C. at the start of the reaction.13. The process as claimed in claim 7 , wherein hydrogen is formed andwherein the peak of hydrogen formation proceeds at a temperature below90° C., and wherein the hydrogen is removed from the reaction space. 14.The process as claimed in claim 12 , further comprising continuing thereaction at a temperature above 90° C.
 15. A precursor for aZiegler-Natta catalyst, comprising the magnesium ethoxide as claimed inclaim 1 .
 16. A ceramic precursor, comprising the magnesium ethoxide asclaimed in claim 1 .
 17. A precursor for book preservation media,comprising the magnesium ethoxide as claimed in claim 1 .